Marine carbon dioxide removal builds on the ocean's natural ability to absorb carbon via biological methods, including the promotion of plankton and seaweed growth, and via chemical or physical processes that directly extract carbon dioxide from seawater. Once carbon is removed from the upper ocean layers, it can be stored in deep-sea sediments, geological reservoirs, or in products designed for long-term storage.
"This is about safeguarding the oceans for a common good. The oceans can be part of the climate solution, but we need to strengthen the way we safeguard them before we scale things up," said Helene Muri, senior researcher at NILU and the Norwegian University of Science and Technology (NTNU). Muri led an expert group commissioned by the European Marine Board that produced a new report released alongside the UN COP30 climate change meeting in Brazil.
The report prioritizes immediate action on emissions reductions using proven techniques. "We know how to cut emissions, and we have lots of methods that work," Muri said. "That has to take top priority." Monitoring, reporting, and verification frameworks for marine carbon removal must be developed to ensure reliable accounting and risk management. Although field tests are underway, many marine removal technologies are experimental.
Net zero targets drive this research, as some CO2 emissions will be difficult or impossible to eliminate in sectors such as aviation and shipping. "We must have a net removal of carbon dioxide from the atmosphere to get to 1.5 C and that means that you will likely have some residual emissions from some sectors, such as shipping and aviation, and some industries," Muri said. "And then you will have relatively large scale removal of carbon dioxide from the atmosphere as well, so that the net is at about between 5 to 10 gigatons of CO2 removed per year towards the end of the century, according to scenarios by the IPCC." For context, global CO2 emissions totaled 42.4 gigatons in 2024.
Land-based carbon removal solutions are in place, including afforestation and direct air capture plants such as those in Iceland. These technologies supplement ocean-based solutions, but many new marine approaches demand verification - especially interventionist strategies like ocean fertilization, which aim to increase carbon uptake through large plankton blooms.
Muri explained, "Ideally, you monitor what is the background state of carbon in the ocean and then implement your project and make sure that you have removed carbon from the atmosphere. You try to monitor how much carbon you have removed and how long it is staying away from the atmosphere. Then you report to an independent party, and it verifies that what you're saying is correct." But "If you're storing it in the ocean, in some form or another, not in a geological reservoir, it's a lot harder to to govern it and also monitor it. The ocean doesn't stay put," she added.
Some companies have started to claim credits for marine carbon removal, but according to Muri, "None of these methods are mature to use if you cannot verify impacts or where the carbon goes, or how long it stays away from the atmosphere." She continued, "If we want to be serious about figuring out if you can do marine carbon dioxide removal in responsible ways that can make meaningful contributions, then we have to get serious about the monitoring, reporting and verification aspects." Crediting systems must be both reliable and scientifically defensible, and environmental impacts reported alongside removal claims.
Ultimately, Muri concluded, "all future scenarios are showing us that we will need carbon dioxide removal in order to reach our most ambitious temperature goal." While marine carbon removal is not a panacea, establishing robust standards is crucial for responsible scaling. "Some people are really hoping to find an answer in the ocean, but in our opinion, we're not there yet."
Research Report: Monitoring, Reporting and Verification for Marine Carbon Dioxide Removal
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Norwegian University of Science and Technology
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